Internal combustion engine with direct injection and sparking plug with precombustion chamber, ignition method and application

ABSTRACT

The invention concerns an internal combustion engine with at least one engine member, the engine member including a combustion chamber ( 4 ) of a combustible mixture with fuel and oxidant components fitted with a compression system ( 9 ), an ignition system ( 7 ) of the combustible mixture by an igniter, sequential let-through devices for the fuel and oxidant components and for the combustion products. According to the invention, the ignition system includes a closed head ( 6 )( 12   a ) substantially spherical enclosing the igniter in a precombustion chamber, the head including a set of orifices ( 5 ) intended to communicate the combustion chamber and the precombustion chamber so that combustible mixture may flow into the precombustion chamber, and at least one of the let-through devices is a direct injector in the combustion chamber for the fuel and/or oxidant components, in all or in part. A method and an application are also described.

The present invention concerns an internal combustion engine withsupercharging and sparking plug with precombustion chamber, an ignitionmethod and an application of the method to the engine. It is intendedfor the industry of fuel, gas engines or others, with two or four-strokeinternal combustion, for motorised vehicles such as motorcycles,automobiles, aircrafts . . . as well as motorised apparatus such asgenerators, toolings or others. Although preferably implemented in apiston/crankshaft engine, it may be applied to a rotary type engine.

Internal combustion engines have been known for numerous years and haveevolved constantly. One considers here, as state of the art, the mostconventional internal combustion engines, i.e. with piston andcrankshaft, enabling to transform an alternate movement of a pistonunder the effect of the combustion of a combustible mixture, into acircular movement. This type of engine includes one or several enginemembers. Each engine member includes a combustion chamber, also calledcylinder, of a combustible mixture with fuel and oxidant components,generally petrol and air, and fitted with a compression system, in sucha case a piston for this type of engine, an ignition system of thecombustible mixture by an electric spark generator as well as sequentiallet-through devices for the fuel and oxidant components and for thecombustion products. The operation of this type of engine, regardlesswhether two or four-stroke is known conventionally and will not bedetailed here.

For some years, it has been sought to optimise the operation of internalcombustion engines and in particular to reduce their fuel consumption aswell as the rejection of combustion products, whereas the latter hadmore and more to become ultimate combustion products and limit theoxidised nitrogen species. To do so, improvements have been introducedto the basic operation of this type of engine. Such improvements concernfor instance the ignition device, additional devices, and modalities forsupplying the oxidant and fuels components, notably with directinjection engines. Progress made in electronics and calculators havealso enabled to improve the operation of engines.

If all these improvements have largely permitted to reduce theconsumption and the emissions, the corresponding engines still exhibitlimitations. In particular, the engines with direct fuel injection aregenerally penalised when preparing the mixture with respect to theinjection engines in intake conduits by problems of homogeneity of themixture in the combustion chamber. Similarly, the engines with directinjection exhibit, in certain configurations of arrangement of theinjector and of the sparking plug, problems of direct impact of the fuelon the electrodes of the sparking plug, hence problems of cold start andof soiling the electrodes of the sparking plug. Finally, the engineswith direct injection are sensitive to the impact of the relatively coldfuel on the walls of the cylinder. Or, for correct initiation(ignition), it may be necessary to have sufficient jet to come close tothe sparking plug, which implies significant walls effect.

Consequently, one knows with the patent EP-0831213 held byDAIMLERCHRYSLER AG, an internal combustion engine with direct injectionwhich uses a spark ignition with an ignition sparking plug. An injectorenables with high pressure to inject directly the fuel components intothe combustion chamber. The sparking plug includes simply a sleeve whichis open in the combustion chamber.

With the applications FR-2.781.840 and FR-2.810.692 one knows particulararrangements of the engine member with precombustion chamber separatedfrom the combustion chamber by a wall not letting through the flamefront generated by the ignition of a combustible mixture in theprecombustion chamber. If this type of device proves efficient toinhibit the pinking phenomenon for high load operation of the engine,one observes however unstable combustion of the engine for a low loadoperation, notably during the idle operation of the engine.

One knows with EP-0957246 a combustion engine of gaseous fuel (CH₄)whereof the control of the ignition is performed by the injection of asmall quantity of liquid fuel in a precombustion chamber.

One also knows devices with supercharging enabling to increase thepressure in the combustion chamber.

The invention intends to provide an ignition system enabling correctcombustion, i.e. with correct combustion output, even in cases ofdetrimental preparation of the mixture. In a preferred embodiment, theignition system replaces the conventional sparking plug on aconventional engine and no specific arrangement is necessary to thecylinder head. The ignition system includes, in its portion in relationwith the combustion chamber, a substantially spherical head drilled withlet-through holes or orifices or passageways, these terms beingequivalent. Inside said head, one finds an igniter, preferably one orseveral electrodes enabling to create a spark by applying a voltagetherebetween.

Thus the invention concerns an internal combustion engine with at leastone engine member, the engine member including:

-   -   a combustion chamber of a combustible mixture with fuel and        oxidant components fitted with a compression system,    -   an ignition system of the combustible mixture by an igniter,    -   sequential let-through devices for the fuel and oxidant        components and for the combustion products.

According to the invention, the ignition system includes a closed headsubstantially spherical with a wall enclosing the igniter in aprecombustion chamber, the head including a set of orifices intended tocommunicate the combustion chamber and the precombustion chamber so thatcombustible mixture may flow into the precombustion chamber, and atleast one of the let-through devices is a direct injector in thecombustion chamber for the fuel and/or oxidant components, in all or inpart.

(The direct injection may indeed concern either single fuels, generallyunder high pressure of the order of 100 bars, or a fuel/oxidantpre-mixture generally under low pressure of the order of 5 to 10 bars).

In various modes for implementing the invention, the following means maybe used individually or according to all their technical possiblecombinations:

the fuel is injected directly and exclusively into the combustionchamber,

the igniter is a generator of electric sparks,

the ignition system is a sparking plug with precombustion chamber,

the ignition system includes a system of introduction of fuel andoxidant components directly in the precombustion chamber,

the ignition system includes a device of introduction enabling directintroduction of a combustible mixture into the precombustion chamber,

the separation wall between the precombustion chamber and the combustionchamber of the head is convex outwardly of the precombustion chamber,

alternatively, the separation wall between the precombustion chamber andthe combustion chamber of the head is concave outwardly of theprecombustion chamber,

alternatively, the separation wall between the precombustion chamber andthe combustion chamber of the head is substantially a polyhedron, acone,

the head of the sparking plug includes a wall of the grid or porousmaterial type,

the separation wall between the precombustion chamber and the combustionchamber of the head is made of a material with thermal conductivitygreater than 10 W/K/m,

the separation wall between the precombustion chamber and the combustionchamber of the head of sparking plug is made of a material with thermalconductivity preferably greater than 30 W/K/m,

the separation wall between the precombustion chamber and the combustionchamber of the head is made of high conductivity copper alloy,

the copper alloy is CuCr1Zr,

the separation wall between the precombustion chamber and the combustionchamber of the head includes a refractory material,

the wall of the head of the sparking plug is covered with a substancefacilitating the reactive combustion des fuel and oxidant componentsand/or the ultimate degradation of the combustion products,

the orifices of the precombustion chamber on the head are cylindricalpassageways,

the orifices of the precombustion chamber on the head are conicalpassageways,

each orifice of the precombustion chamber on the head has a diametersmaller than or equal to 3 mm,

the orifices of the precombustion chamber of the head are minimum threein number,

the orifices of the precombustion chamber of the head are arranged onthe head so that the combustion of the combustible mixture in theprecombustion chamber induces jets of matter through the orifices to thecombustion chamber distributed to ensure homogeneity of the combustionof the combustible mixture substantially in the whole combustionchamber,

the compression system is a piston in a cylindrical combustion chamberwith central axis, the injector being arranged substantially axiallyopposite the piston and the ignition system laterally with respect tothe injector, and the orifices are predominantly arranged towards theaxis,

the compression system is a piston in a cylindrical combustion chamberwith central axis, the ignition system being arranged substantiallyaxially opposite the piston and the injector laterally with respect tothe ignition system, and the orifices are distributed regularly on thesurface of the head,

the compression system is a piston in a cylindrical combustion chamberwith central axis, the injector and the ignition system being arrangedlaterally with respect to said axis, and the orifices are predominantlyarranged towards the axis,

the head is arranged on a portion of the path of the fuel componentsinjected so that said head may be wetted by said fuel components duringthe direct injection thereof,

at least one orifice has dimensions of passageway letting through aflame front from the precombustion chamber to the combustion chamber,

each orifice letting through the flame front has a diameter rangingbetween 1 and 3 mm,

at least one orifice has dimensions of passageway not letting through aflame front from the precombustion chamber to the combustion chamberwhile letting through unstable species resulting from the combustion inthe precombustion chamber in order to enable self-ignition of thecombustible mixture of the combustion chamber, (the head may thereforeinclude orifices of both previous types, i.e. letting through and notletting through the flame front)

the number of orifices enabling the propagation of a flame frontprovided in the head of the precombustion chamber body varies from 1 to5 and preferably is 1 and the number of orifices not enabling thepropagation of a flame front varies from 1 to 20, preferably from 3 to15,

the set of orifices has dimensions of passageway not letting through theflame front from the precombustion chamber to the combustion chamberwhile letting through unstable species,

each orifice not letting through the flame front has a diameter smallerthan 1 mm,

each orifice not letting through the flame front has a diameter rangingbetween 0.5 and 1 mm,

each orifice has a length smaller than its diameter,

the engine includes moreover means enabling to re-inject with theoxidant components a portion of the combustion products,

the engine includes moreover means enabling to compress the oxidantcomponents upstream of the engine member in order to enablesupercharging,

the injector has multiple jets, with jets directed towards the head,

the jets are sequentially distributed with time,

the fuel is exclusively liquid, notably petrol.

The invention also concerns an ignition method of an internal combustionengine having at least one engine member, the engine member including:

a combustion chamber of a combustible mixture with fuel and oxidantcomponents fitted with a compression system,

an ignition system of the combustible mixture by an igniter,

sequential let-through devices for the fuel and oxidant components andfor the combustion products.

According to the method of the invention:

one implements an ignition system including a closed head substantiallyspherical with a wall enclosing the igniter in a precombustion chamber,the head including a set of orifices intended to communicate thecombustion chamber and the precombustion chamber so that combustiblemixture may flow into the precombustion chamber,

one introduces directly in the combustion chamber all the fuel and/oroxidant components through one of the let-through devices which is adirect injector,

one introduces moreover at least of the oxidant components in saidcombustion chamber in order to form the combustible mixture,

-   -   one causes an ignition of the combustible mixture in the        precombustion chamber by the igniter, the orifices of the        precombustion chamber enabling the ignition of the combustible        mixture of the combustion chamber.

The previous steps are also implemented in a method characterised inthat one lets through the orifices of the unstable species resultingfrom the combustion in the precombustion chamber in order to enableself-ignition of the combustible mixture of the combustion chamberwithout however letting through the flame front from the precombustionchamber to the combustion chamber.

The invention also concerns an application of the methods according tothe previous features to the engine according to one or several of thefeatures of engines listed previously.

The invention concerns finally a sparking plug with precombustionchamber for implementation in the engine of the invention and accordingto one or several of the corresponding features listed previously.

Among the advantages provided by the invention, the ignition system withprecombustion chamber enables to obtain stabler combustion, even in thecase of a little homogeneous mixture. Indeed, on the one hand severalflame fronts reach different zones of the combustion chamber and on theother hand, the radicals emitted by the orifices of the igniter seed thecombustion chamber in different points and under the effects combined ofthe pressure and of the temperature generated by the rising piston,these precursors ignite the mixture in different points of thecombustion chamber. The probability of having precursors in a zonefavourable to the initiation of the combustion is therefore much higherthan in the case of a conventional sparking plug. Moreover, the wall ofthe precombustion chamber protects the electrodes from the impact ofliquid fuel thereon, hence a better behaviour at cold start andreduction in the soiling of the sparking plug. Then, it is possible touse an injector jet wetting directly the walls of the precombustionchamber of combustion, which promotes the rising of carburized mixtureinside the precombustion chamber. Thus may bring beneficial effects atthe start and the initiation generally.

Finally, in the case of layered combustion, the injection of fuel on thehead of the hot igniter enables to increase the Al/AA robustness by theeffect of the vaporisation of the fuel in the vicinity of the electrodes(Al corresponds to the injection advance and AA to the ignitionadvance). The other advantages provided by the present invention are theprotection of the electrode(s) of the sparking plug. The probability ofpresence of carburized mixture in the vicinity of the electrodes is thushigher.

The invention may also be implemented advantageously in the case ofinternal combustion engines with controlled ignition and heavilysupercharged as will be seen below in detail.

The present invention will now be exemplified with the followingdescription and in relation with:

FIG. 1 which represents as seen in the precombustion chamber theprogression of the combustion generated by a spark,

FIG. 2 which represents as seen in the combustion chamber the differentorifices of the head of sparking plug,

FIGS. 3, 4, 5, 6 which represent seen as a sectional view, a cylinderaccording to different operating phases of the engine of the invention,

FIG. 7 which represents an example of embodiment of an ignition systemwith a sparking plug seen as a partial sectional view,

FIG. 8 which represents an example of embodiment of a head of theignition system.

The ignition systems whereof the igniter is a discharger intended toproduce electric sparks, of the sparking plug type, may show differentconfigurations in relation to the type of engine and/or to theperformances desired. For instance the sparking plugs may be of variouslengths. The invention which implements a sparking plug withprecombustion chamber may employ different configurations of sparkingplugs and one will give a particular example thereof at the end of thedescription. In the invention, the sparking plug includes aprecombustion chamber according to features which will now be specified.

Experiments have been conducted on several configurations of ignitionsystems according to the invention. The features of the sparking plugwith precombustion chamber more particularly assessed are:

Volume: 700 mm³

Section passage: 5.1 mm²

S/V ratio (mm⁻¹): 7.4×10⁻³ mm⁻¹

(S being the sum of the sections of the passageways and V the volume ofthe precombustion chamber)

Inter-electrode distance: 0.7 mm.

As regards the SN ratio, it is a quality indicator. The lower thisratio, the better the output of use of the oxidant and of fuel. Theoptimum case is that of the spherical precombustion chamber.

The ignition system of the sparking plug type with precombustion chamberof the invention is a component which does not require any particularmachining of the engine. The implantation may take place in aconventional engine sparking plug well since its diameter may be smallerthan or equal to 14 mm. The volume of the precombustion chamber mayrange between 0.2 and 2 cm³. Preferably, the precombustion chamber has avolume smaller than 1.5 cm³, generally ranging between 0.5 cm³ and 1.5cm³. Generally, the ratio between the volume of the precombustionchamber and the dead volume of the main chamber varies between 0.1 and5%, preferably between 0.1 and 2%. The form of the head of the ignitionsystem is preferably a spherical cap.

Optionally, the ignition system may moreover include an inlet enablingto supply directly the precombustion chamber with a combustible mixtureformed upstream or to introduce fuel, the air being then mixed with thefuel in the precombustion chamber.

The ignition system includes in its portion in relation with thecombustion chamber, a spherical head drilled with holes or orifices orpassageways, these terms being equivalent in the context of theinvention. Inside said head, one finds the igniter in the form of one orseveral electrodes enabling to create a spark by applying a voltagetherebetween.

When developing the ignition system, several configurations of materialhave been tested for the wall of the precombustion chamber, i.e.: Steel35CD4; alloy Ni—Fe—Cr, copper alloy whereof brass or copper-nickel-zincalloys or with nickel or aluminium; high conductivity copper alloyCuCr₁Zr. The best results have been obtained with the latter material.The alloy CuCr₁Zr is a grade of the alloy CRM16x with a ratedcomposition Cr>0.4%, Zr from 0.022% to 0.1% and the remainder is copper.

As stated above, the precombustion chamber may be made of a materialhaving a thermal conductivity greater than 10 W/K/m and preferablygreater than 30 W/K/m. One may thus use materials whereof the thermalconductivity may reach 350 W/K/m. The use of such a material, preferablya copper alloy, enables to evacuate the energy at the wall ofprecombustion chamber and thus to make up for the occurrence of hotpoints at the precombustion chamber. For instance, for the materialsubject to in-depth experiments, the alloy CuCr1Zr, the thermalconductivity at 20° C. of 320 W/K/m.

For exemplification purposes for other copper-based usable materials,one may consider a grade of brass: CUZn37 of conductivity: 113 W/K/m.

The following table shows different binary brasses, copper-nickels,copper-aluminium and copper-nickel-zinc alloys being usable as materialfor the precombustion chamber body. The level of thermal conductivity aswell as the mechanical handling at high temperature (450-1000 K)determines the selection of the material.

Brass: Physical Properties Property (composition according to thestandard NF A 51-101) Cu Zn Cu Zn Cu Zn Cu Zn Cu Zn Cu Zn Cu Zn Cu Zn 510 15 20 30 33 36 40 Thermal 234 188 159 138 121 117 117 121conductivity at 20° C. [W/(m · K)]

Copper-Nickel-Zinc Alloys: Physical Properties Property (compositionaccording to the standard NF A 51-101) Cu Ni 10 Cu Ni 18 Cu Ni 10 Cu Ni12 Cu Ni 15 Cu Ni 18 Cu Ni 18 Zn 42 Zn 19 Zn 27 Zn 24 Zn 21 Zn 20 Zn 27Pb 2 Pb 1 Thermal 38 38 34 29 25 34 25 conductivity at 20° C. [W/(m ·K)]

And finally the alloys:

-   -   Copper-nickel: 21 W/(m·K) (Cu Ni 44 Mn) to 63 W/(m·K) (Cu Ni 5        Fe)    -   Copper-aluminium: 75 to 84 W/(m·K) (Cu Al 5, Cu Al 6), 38 to 46        W/(m·K) (Cu Al 10 Fe 5 Ni 5)    -   This data is derived from “Technique de l'ingénieur”, Volume MB        5—Etude et propriétés des métaux M437

This type of sparking plug with precombustion chamber is used preferablywith an engine showing optimised permeability of the cylinder head tothe detriment of the aerodynamics of the combustion chamber. Indeed, thecombustion mode resulting from the use of the sparking plug withprecombustion chamber enables sufficient combustion speed to dispensewith an increase in the combustion speed via the aerodynamics of thecombustion chamber.

FIG. 1 represents therefore, as seen in the precombustion chamber 1, theprogression of the combustion 2 generated by a spark 3.

FIG. 2 represents therefore, as seen in the combustion chamber 4, thedifferent orifices 5 of the wall of the head 6 of sparking plug enablingcommunications between the precombustion chamber 1 and the combustionchamber 4, also called main chamber. Thanks to these communications, onthe one hand, combustible mixture flows from the combustion chambertowards the precombustion chamber and, on the other hand, after ignitionin the precombustion chamber, the combustible mixture of the combustionchamber may finally ignite. The disposition of the orifices enablessubstantially homogeneous distribution of the flame front and/or of theunstable species which enable the ignition of the combustible mixture ofthe combustion chamber.

FIGS. 3, 4, 5, 6 represent an engine member seen as an axial section ofa piston 9 and going through a injector 8 and a sparking plug 7. Theother inlet and exhaust members for sequential passageways of theoxidant components (possibly fuel) and for the combustion products, arenot detailed therein. On FIG. 3, the phase of injection of the fuelcomponents by the injector 8 is in progress and a portion of fuels willwet the head 6 of the sparking plug 7 which surrounds the precombustionchamber. on FIG. 4, the engine being hot, the fuels are vaporisedsimultaneously on the piston 9 which includes a <<piston bowl>> and onthe head 6 of the sparking plug 7. On FIG. 5, the phase of compressionhas begun and combustible mixture flows from the combustion chamber 4towards the precombustion chamber 1 of the sparking plug 7. On FIG. 6,the phase of combustion has begun from the precombustion chamber 1wherein a spark has been produced and by passing through the orifices 5of the head 6, of the flame front and/or according to the type oforifice, of the unstable species for propagation to the combustionchamber 4.

Preferably the sparking plug and its head are a single component whichreplaces a traditional sparking plug which does not require anymodification of the cylinder head passageway for the sparking plug. Theignition system is thus formed of a device replacing the conventionalsparking plug. One also contemplates that the system generating thespark be modified in relation to the form of the head and, for instancethat the central electrode moves forward further in the head and comescloser to the wall of the former so that the electric arc is formedbetween the central electrode and the wall of the head. It should beunderstood that in such a case, the wall must include a conductivematerial of the electricity for the spark current to return to theground. One also contemplates that the head of sparking plug be aremovable part, for instance by screwing, and which may be unscrewed togain access to the electrode(s) of the sparking plug for possible gapadjustment or inspection. In the latter case, it may be desirable thatthe head extends laterally towards the rear in a screwing zone on thecylinder head to be held and may not be unscrewed and no fall in thecombustion chamber further to the vibrations of the engine.

It should be understood that the examples given are purely illustrativeand that the invention may be provided according to diversepossibilities. It has been observed thus that a head with orifices ofboth types could be used, i.e. letting through and not letting throughthe flame front. Similarly, the orientations orifices may be optimisedin relation to the relative disposition of the different members in theengine.

Thus, among the applications of the invention one may quote superchargedengines. Engine tests for assessing the potential of sparking plugs withprecombustion chamber have been conducted on heavily superchargedengines, i.e. up to more than 15 bars. These tests have enabled to putin evidence a path of improvement regarding full load enrichment(PME=efficient average pressure=13 bars) when using sparking plugs withprecombustion chamber.

Supercharged engines require thermal protection of the turbine. Indeed,the former is exposed directly to the flux of hot gases coming out ofthe engine while the turbine shows a maximum destructive, limited,injected temperature. Usually, to remedy this shortcoming, one resortsto enrichment by addition of fuel to limit the temperature of the gasesburnt at the outlet of the engine. Indeed, the surplus of fuel thusprovided may not burn since the quantity of air present in the cylinderis insufficient (the quantity of air present in the cylinder onlyenables to burn the fuel equivalent to the richness 1), and this surplusof fuel while evaporating (latent evaporation heat) enables the load tocool down. The gases come out therefore less hot from the cylinder.However, this effect is proportional to the surplus of petrol providedand said petrol is only used for cooling down the gas which causes anincrease in consumption

One has shown during experiments on this type of supercharged enginenotably the following improvements in an engine according to theinvention: a reduction in full load enrichment, total or partialinhibition pinking phenomenon with a volumetric ratio ranging between 8and 14, a better use of the air.

As stated above in introduction, this diminution effect in the pinkingis notably perceptible in the case of the operation of the engine onhigh load. To give an order of magnitude, by low load operation of theengine is meant the operating range of the engine from idle to a quarterof the full load of the engine, preferably the range from idle to 10% ofthe full load in the case of an atmospheric engine and the range fromidle to 5% of the full load in the case of an heavily superchargedengine.

In an alternate embodiment of the head of the ignition system, oneimplements orifices in the wall of the head which have a differentialeffect, letting through or not letting through the flame front inrelation to the load of the engine. This effect may be obtained forinstance by at least one orifice enabling the propagation of a flamefront on low load and at least one orifice not enabling the propagationof a flame front under any load conditions or, then, through simply atleast one orifice enabling the propagation of a flame front on low load.In the case of a low load operation of the engine, the flame front mayflow from the precombustion chamber to the main combustion chamber bymeans of the passageway(s) enabling the propagation of a flame front andone causes thus the ignition of the main combustible mixture via a flamefront. In the case of an operation on high load of the engine, thestructure orifices which let through the flame front on low load is suchthat, on high load, the flame front does not flow any longer, saidorifices causing an extinction of the flame front and these are then theunstable compounds from the combustion of the combustible mixture to theprecombustion chamber which induce mass self-ignition of the maincombustible mixture seeded with the unstable compounds in the mainchamber.

One may explain this phenomenon as follows. Taking into account thesmall quantity of air/fuel mixture in the precombustion chamber in thecase of low supercharge, the pressure rise in the precombustion chamberat the ignition is significantly less violent than in the case of highloads and the flame front obtained by the combustion of the mixture inthe precombustion chamber may, thanks to the passageway of largediameter propagate in the main combustion chamber. Said continuouspropagation of the flame front between precombustion chamber and maincombustion chamber causes stability on low load similar to theconventional case of the controlled ignition engines. In the case ofhigh loads, the quantity of carburized mixture in the precombustionchamber is from 3 to 7 times greater than the little supercharged case.Consequently, during the combustion of the mixture in the precombustionchamber, the pressure rise is significantly greater. The differentialpressure between the precombustion chamber and the main chamber preventsthe propagation of the flame front from the precombustion chamber to themain chamber. Nevertheless, the passageways let flow the flux ofunstable compounds from the precombustion chamber to the main chamberand, during the rising of the piston, the compression produces massself-ignition of the main mixture.

It should be understood the one may also use orifices letting through ornot letting through the flame front regardless whether under allconditions or not to obtain differential effects this times in volume,certain types of orifices being arranged on the head preferably to havecombustion-triggering effects in a more particular zone of thecombustion chamber. These differential effects in relation to the loadand of the volume may be combined by a particular arrangement oforifices of different structures on the head.

In another alternative embodiment of the head of the ignition system,possibly combined to the latter, the internal and/or external faces ofthe wall of the head of the precombustion chamber as well as, possibly,the walls of orifices, are coated with a refractory coating layer, suchas coating layers of Al₂O₃, ZrY (not necessarily stoichiometric) andTiB₂. The thickness of these coating layers ranges generally between 0.5and 100 μm, preferably 1 to 50 μm. One increases thus the efficiency ofcombustion in the precombustion chamber and improves the low loadoperation, in particular in the case of heavily overboosted engines.

The implementation of the invention in a supercharged engine enablestherefore to limit the enrichment on high load since the combustion isfaster and terminates sooner in the engine cycle. The gas derived fromthe combustion exit therefore not so hot from the cylinder since thetime between the end of combustion and the valve opening is longer. Theenrichment necessary to the protection of the turbine may therefore bereduced, hence smaller consumption on this type of supercharged enginewith respect to a conventional ignition with electrode type sparkingplug.

As stated above, different configurations of sparking plugs withprecombustion chamber may be used. There is given on FIG. 7 a particularexample of sparking plug with precombustion chamber which includes abody in the extension of the head. The sparking plug 7 is screwed in athread 10 a of the cylinder head 10 closing a cylinder of an internalcombustion engine whereof only a portion has been represented. Thesparking plug 7 includes a body 12 of precombustion chamber 1 generallytubular in shape and comprising a head 12 a generally convex in shape,preferably having the form of a spherical cap. The head 12 a of the body12 of precombustion chamber 1 forms a separation wall between thecombustion chamber 4 and the precombustion chamber 1. The precombustionchamber 1 includes the igniter comprising a central electrode 13 and aground electrode 14. The head 12 a forming the separation wall betweenthe combustion chamber 4 and the precombustion chamber 1 is providedwith different let-through orifices 5, represented more in detail onFIG. 8.

In this example, the orifices 5, generally cylindrical in shape,comprise a passageway 5 a, having a large diameter, i.e. a diametergreater than 1 mm, generally ranging between more than 1 mm and 3 mm anda series of orifices 5 b to 5 i (7 in the embodiment of FIG. 8) having asmall diameter, i.e. smaller than or equal to 1 mm. Generally, thelength of the passageways is smaller than 1 mm and they are hereoriented according to radii of the hemispherical head 12 a. One has alsoseen that the orientation and/or the structure orifices may be suited tothe particular configuration of the element of the engine.

Although one has represented a single orifice 5 a of diameter greaterthan 1 mm (preferred embodiment), the head 12 a may include severalorifices of large diameter. However in certain applications, as alreadyseen with the differential effects orifices on the flame front inrelation to the load, the number and the dimension orifices must be suchthat no flame front may propagate from the precombustion chamber to thecombustion chamber when the engine operates on high load.

It should be understood that the examples given are purely illustrativeand that it is possible to implement the invention according to diversemodalities without departing from its general framework.

1. An internal combustion engine with at least one engine member, theengine member including: a combustion chamber of a combustible mixturewith fuel and oxidant components fitted with a compression system, anignition system of the combustible mixture by an igniter, sequentiallet-through devices for the fuel and oxidant components and for thecombustion products, wherein the ignition system includes a closed headsubstantially spherical with a wall enclosing the igniter in aprecombustion chamber, the head including a set of orifices intended tocommunicate the combustion chamber and the precombustion chamber so thatcombustible mixture may flow into the precombustion chamber, and atleast one of the let-through devices is a direct injector in thecombustion chamber for the fuel and/or oxidant components, in all or inpart, the fuel being injected directly and exclusively in the combustionchamber.
 2. An engine according to claim 1, wherein at least one orificehas dimensions of passageway letting through a flame front from theprecombustion chamber to the combustion chamber.
 3. An engine accordingto claim 1, wherein at least one orifice has dimensions of passagewaynot letting through a flame front from the precombustion chamber to thecombustion chamber while letting through unstable species resulting fromthe combustion in the precombustion chamber in order to enableself-ignition of the combustible mixture of the combustion chamber. 4.An engine according to claim 3, wherein the set of orifices havedimensions of passageway not letting through the flame front from theprecombustion chamber to the combustion chamber while letting throughunstable species.
 5. An engine according to claim 3, wherein eachorifice not letting through the flame front has a diameter smaller than1 mm.
 6. An engine according to claim 3, wherein each orifice has alength smaller than its diameter.
 7. An engine according to claim 1,wherein the separation wall of the head between the precombustionchamber and the combustion chamber is made of a material with thermalconductivity greater than 10 W/K/m.
 8. An engine according to claim 1,wherein the separation wall of the head between the precombustionchamber and the combustion chamber is made of high conductivity copperalloy (CuCr1 Zr).
 9. An engine according to claim 1, wherein theorifices of the head are minimum three in number.
 10. An engineaccording to claim 1, wherein the compression system is a piston in acylindrical combustion chamber with central axis, the injector beingarranged substantially axially opposite the piston and the ignitionsystem laterally with respect to the injector, and the orifices arepredominantly arranged axially to ensure homogeneity of the combustionof the combustible mixture substantially in the whole combustionchamber.
 11. An engine according to claim 1, wherein the compressionsystem is a piston in a cylindrical combustion chamber with centralaxis, the ignition system being arranged substantially axially oppositethe piston of the injector laterally with respect to the ignitionsystem, and the orifices are distributed regularly on the surface of thehead to ensure homogeneity of the combustion of the combustible mixturesubstantially in the whole combustion chamber.
 12. An engine accordingto claim 1, wherein the compression system is a piston in a cylindricalcombustion chamber with central axis, the injector and the ignitionsystem being arranged laterally with respect to said axis, and theorifices are predominantly arranged axially to ensure homogeneity of thecombustion of the combustible mixture substantially in the wholecombustion chamber.
 13. An engine according to claim 1, wherein the headis arranged on a portion of the path of the fuel components injected sothat said head may be wetted by said fuel components during the directinjection thereof.
 14. An engine according to claim 1, wherein theignition system with its head are a single component which replaces atraditional sparking plug and which does not require any modification ofthe passageway of cylinder head.
 15. An engine according to claim 1,wherein the fuel is exclusively liquid, notably petrol.
 16. A method ofignition of an internal combustion engine having at least one enginemember, the engine member including: a combustion chamber of acombustible mixture with fuel and oxidant components fitted with acompression system, an ignition system of the combustible mixture by anigniter, sequential let-through devices for the fuel and oxidantcomponents and for the combustion products, wherein one implements anignition system including a closed head substantially spherical with awall enclosing the igniter in a precombustion chamber, the headincluding a set of orifices intended to communicate the combustionchamber and the precombustion chamber so that combustible mixture mayflow into the precombustion chamber, and one introduces directly in thecombustion chamber the fuel and/or oxidant components, in all or inpart, through one of the let-through devices which is a direct injector,the fuel being injected directly and exclusively in the combustionchamber, one introduces moreover at least some oxidant components insaid combustion chamber in order to form the combustible mixture, onecauses an ignition of the combustible mixture in the precombustionchamber by the igniter, the orifices of the precombustion chamberenabling the ignition of the combustible mixture of the combustionchamber.
 17. A method according to claim 16, wherein one lets throughthe orifices some unstable species resulting from the combustion in theprecombustion chamber in order to enable self-ignition of thecombustible mixture of the combustion chamber without however lettingthrough the flame front from the precombustion chamber to the combustionchamber.
 18. A method according to claim 16, wherein the engine is aninternal combustion engine with at least one engine member, the enginemember including: a combustion chamber of a combustible mixture withfuel and oxidant components fitted with a compression system, anignition system of the combustible mixture by an igniter, sequentiallet-through devices for the fuel and oxidant components and for thecombustion products, wherein the ignition system includes a closed headsubstantially spherical with a wall enclosing the igniter in aprecombustion chamber, the head including a set of orifices intended tocommunicate the combustion chamber and the precombustion chamber so thatcombustible mixture may flow into the precombustion chamber, and atleast one of the let-through devices is a direct injector in thecombustion chamber for the fuel and/or oxidant components, in all or inpart, the fuel being injected directly and exclusively in the combustionchamber.